[EC-364] Expose key getters on CryptoService (#3170)

* Move resolveLegacyKey to encryptService for utf8 decryption

* Deprecate account.keys.legacyEtmKey

Includes migration to tidy up leftover data

* Use new IEncrypted interface

libs/common/src/enums/stateVersion.ts

@@ -4,5 +4,6 @@ export enum StateVersion {
   Three = 3, // Fix migration of users' premium status
   Four = 4, // Fix 'Never Lock' option by removing stale data
   Five = 5, // Migrate to new storage of encrypted organization keys
-  Latest = Five,
+  Six = 6, // Delete account.keys.legacyEtmKey property
+  Latest = Six,
 }